Understanding the decisions that individuals make about their health is an important ingredient in understanding the differences in health outcomes across demographic and socioeconomic groups, and health improvements over time. This proposal examines behavioral decisions that individuals make affecting their health and attempts to explain the reasons for differences across individuals. Our specific aims are: (1) to document and compare trends in health behaviors across demographic groups, and to examine the correlation of favorable and adverse health behaviors across people; (2) to develop theoretical models of decision-making that incorporate different decision processes, and to catalogue the implications of these models; and (3) to use time series data over the past forty years and recent panel data sets, to determine which theories are consistent with the data.